The invention is related to the field of fiber reinforced plastic tubes. Depending on the nature of the fibers applied, such tubes usually have a high strength. For instance, polyester fibers make the tubes in question suitable for the transport of high pressure liquids and gasses. Examples thereof are crude oil and natural gas, which may comprise aggressive components. Such components may be detrimental to steel pipes, for which reason it is desirable to use fiber reinforced tubes having a proper liner which can withstand the aggressive nature of such fluids.
The strength of the tube therefore depends heavily on the fiber reinforcement. As mentioned, the tubes comprise an inner liner so as to convey the fluids. Onto the liner, the fiber reinforcement layer is applied, and finally the coating layer is applied onto the fiber reinforcement layer. This fiber reinforcement layer may be carried out in various shapes. As an example, the fiber reinforcement layer may be a braided layer. Alternatively, the fibers may be embedded in a tape which is wound around the liner according to a helical shape. Also, the fibers may be wound onto the liner according to various plies and winding angles.
Due to the nature of the plastics and the fibers used, the tube has a stiff character in such a way that it maintains its circular shape, also when exposed to moderate external pressure loading. Depending on the diameter of the tube, this stiffness will resist the bending of the tube to a greater or lesser extent. Generally, it is still feasible to wind a tube of relatively small cross sectional diameter onto a reel, the diameter of which however must not be too small as otherwise the tube will buckle or kink while being wound onto the reel.
The step of winding the tubes on a reel is highly desirable having regard to the fact that it is thereby made possible to supply a great uninterrupted tube length. Tubes of a great length have the advantage that relatively few couplings need to be made to make up a complete trajectory, which is beneficial for both the reliability of such trajectory and for limiting the cost thereof. It will however be clear that the maximum dimensions of reel with a tube wound thereon are limited, having regard to the requirements which are imposed when using road transport. As a tube of relatively large cross sectional diameter has by its very nature a high resistance against bending, it is hardly feasible to wind such tube onto a reel which, in view of road transport, has moderate dimensions. This means that a tube with relatively large diameter is usually supplied in straight sections of limited length. As mentioned, this has disadvantages both in view of the cost of the trajectory obtained and the cost thereof.